Rep. Devin Nunes, once sidelined by an ethics inquiry from leading the House Intelligence Committee's Russia probe, is reasserting the full authority of his position as chairman just as the GOP appears poised to challenge special counsel Robert S. Mueller III's investigation of possible coordination between the Trump campaign and Russian officials.

The California Republican was cleared in December of allegations he improperly disclosed classified information while accusing the Obama administration of exposing the identities of Trump affiliates on surveillance reports. Since clearing his name, Nunes has stepped up his attacks on Mueller's team and the law enforcement agencies around it, including convening a group of Intelligence Committee Republicans to draft a likely report on "corruption" among the investigators working for the special counsel.

Although Nunes has not officially wrested his panel's Russia probe back from the Republicans he deputized to run it, the chairman's reemergence as a combative Trump loyalist has raised alarm among Democrats that the future of the investigation may be clipped short or otherwise undermined. Even some of Nunes's GOP allies have expressed concern about his tactics, prompting rare public warnings that he should temper his attacks on federal law enforcement.

"I'm interested in getting access to the information and not the drama," Rep. Trey Gowdy (R-S.C.) said last month, when Nunes began threatening contempt citations for FBI Director Christopher A. Wray and Deputy Attorney General Rod J. Rosenstein in the wake of revelations that former Mueller team members had exchanged ­anti-Trump texts.

More recently, Gowdy said that his "heart would be broken" if Nunes follows through on reported plans to issue a corruption exposé about the FBI, citing concerns that issuing such a report outside the context of a comprehensive investigation of the Justice Department could prove damaging to law enforcement.

Gowdy, a member of the Intelligence panel who also chairs the House Committee on Oversight and Government Reform, suggested that Nunes has taken some of these steps without the express blessing of House Speaker Paul D. Ryan (R-Wis.), who has been involved in crafting the GOP's multipronged approach to examining a string of allegations from Russian election interference to alleged mismanagement at the nation's top law enforcement agencies.

A spokesman for Nunes declined to comment.

But Nunes's moves coincide with what Democrats say is a coordinated GOP effort to shutter the House Intelligence Committee's Russia probe, publicly absolve President Trump of the most serious allegations against him, and refocus the House's resources against the law enforcement officials, such as Mueller, who continue to investigate Trump.

For months, Democrats have kept an unofficial count of the ways they say Nunes worked behind the scenes during the time he was under ethics investigation to slow or stymie the Intelligence Committee's Russia probe. Nunes never relinquished his sole, unchecked authority to sign off on subpoenas even as he handed the day-to-day operations to Reps. K. Michael Conaway (R-Tex.), Gowdy and Thomas J. Rooney (R-Fla.). People familiar with the committee's work estimated that Nunes's effective veto cost Democrats dozens of requests for interviews and documents that were never sent out, despite repeated entreaties from the minority side.

This includes requests for subpoenas to obtain additional testimony from key figures in the probe who Democrats say were not forthcoming enough in interviews — among them Attorney General Jeff Sessions and Trump's son Donald Trump Jr. Democrats surmise they might have compelled them to return if not for Nunes's resistance.

Nunes, who is chairman of the House Intelligence Committee, speaks on Capitol Hill in October. Surrounding him are Rep. Peter King, (R-N.Y.), left, and Rep. Ron DeSantis (R-Fla.). (Susan Walsh/AP)

Republicans have dismissed such complaints as political posturing. Conaway said that he has received every subpoena approval he has requested from Nunes, while others pointed to the steady stream of witnesses who sat for interviews with the Intelligence Committee — and challenged Democrats to name who they say is missing.

"Adam's list is pretty much every character in any Dostoevsky or Tolstoy novel," Gowdy said, referring to the Intelligence panel's top Democrat, Rep. Adam B. Schiff of California. "I get the intrigue and the mystery of these unusual-sounding names, but at some point you have to tie it back to what we're looking at."

"You can interview anybody that's ever met a Russian in the government and it's not going to get you any closer," said Rooney. "Ten months, how many witnesses? I want to know, ask them how much longer they want to go. How many more witnesses do they need to hear, and specifically which witnesses, and why?"

But to Democrats, the march of witnesses in and out of the committee's secure interview facility in the U.S. Capitol building basement has provided little assurance the probe is being run properly.

The packed schedule, sometimes featuring two or three overlapping interviews per day, has sparked complaints from Democrats that it is impossible to fully prepare for or monitor the investigation's progress. Even when members are able to focus on one witness at a time, people familiar with the probe said, relevant requested documents often fail to materialize until after the interview has concluded — and the interviewees are hardly ever invited back.

The order of interviews has also been a point of ongoing dispute. While Senate Intelligence Committee leaders boast of a methodical process that starts with peripheral players and builds to key witnesses, the House Intelligence Committee's order is comparatively haphazard and unstructured — almost designed, critics say, to give the probe a "veneer of respectability" while effectively giving investigators whiplash.

Nunes's hand in such decisions was never direct, people familiar with the probe said. During the period he was under an Ethics Committee investigation, he never once attended a closed-door meeting at which the Russia probe was discussed — something both his allies and critics attest to. But at least one of his senior committee staff members was always present at such sessions to help update members, question witnesses and otherwise run the probe, multiple people said. Even Republicans acknowledge it was difficult to distinguish between staff members' allegiance to the committee and their loyalties to Nunes.

"I don't know where his staff ends and HPSCI" begins, Gowdy said, referring to the House Intelligence committee by its official acronym. "Some of them are apolitical nonpartisan members of his staff, and I'm not smart enough to know who's what."

Once the House Intelligence Committee concludes its investigation, it is unclear what precise role remains for Nunes in the House GOP's continued push to investigate allegations of bias and other misconduct in law enforcement. The House Committee on Oversight and the Judiciary Committee have already launched an inquiry into the FBI's handling of the Hillary Clinton email probe. And a joint investigation by Nunes and Gowdy into the Justice Department and FBI's review of circumstances surrounding an Obama-era deal giving Russia a stake in the American uranium market seems to have lost its initial momentum.

If there is one aspect of the Russia probe that seems destined to outlast the House Intelligence Committee's preferred timeline, it is Nunes's investigation of Fusion GPS, the firm behind a dossier detailing Trump's alleged connections to Russian officials, financiers and exploits in Moscow. Nunes's subpoena of the firm's bank records is caught up in a court battle, and the chairman's staff is in touch with the office of Sen. Charles E. Grassley (R-Iowa), according to the senator, who is also looking into reports that the Clinton campaign and the Democratic Party paid for research that ended up in the dossier's pages.

The dossier continues to be a focus of the president in tweet storms seeking to discredit Mueller's probe. Most recently, he blasted the FBI for focusing on the "Crooked Hillary pile of garbage" dossier "as the basis for going after the Trump Campaign." In recent weeks, he has also tweeted encouragement of Nunes's efforts to unearth information about the dossier from the "deep state."

Nunes, meanwhile, appears to have made up his mind about the House Intelligence Committee probe into the allegations surrounding Trump and Russia, expressing his convictions in an interview with Fox News.

"We have no evidence of Russia collusion between the Trump campaign" and Russia, Nunes said.

Karoun DemirjianKaroun Demirjian is a congressional reporter covering national security, including defense, foreign policy, intelligence and matters concerning the judiciary. She was previously a correspondent based in The Post's bureau in Moscow. Follow